Process of preparing translucent cellulosic sheeting



E. H. HILBDRN PROCESS PREPARING TRANSLUCENT CELLULOSIC SHEETING April 30, 1957 Filed- June 17; 1950 FIG. 1.

4m in Edwih' H. H ilborn Zmventor 09M 3.0 M Vmu Qttorneg United States Patent PROCESS OF PREPARING TRANSLUCENT CELLULOSIC SHEETING Edwin H. Hilborn, Rochester, N. Y., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application June 17, 1950, Serial No. 168,327

6 Claims. (Cl. 117-10) This invention relates to a process for preparing translucent type sheeting and the resultant product. More particularly, this invention concerns an improved method of securing a matte effect on sheeting by a chemical, physical reaction.

As is known in the art, there is available considerable quantities of film, plates or sheets manufactured from various cellulosic and the like materials. These items, which for convenience of reference herein, will be referred to as sheets, may have a glossy or transparent surface. For a number of purposes it is desirable that such sheet products be provided with a matte, translucent, or ground glass type of surface. Therefore, a number of methods have already been proposed in the industry for securing such a matte surface upon sheeting. One prior art method involves subjecting the transparent or the like glossy sheeting to some type of action that softens the surface of the sheet, after which the softened surface is contacted with a roll exemplified by a sand blasted or the like embossing roll for securing an embossed or a matte effect upon the sheet. The softening of the surface of the sheet is accomplished by the use of solvents or warming. However, such methods have the disadvantage that any scratches or other imperfections on the sand blasted roll produces repeating defects on the processed sheeting. This is obviously apparent in that a roll contact against the sheet, of course, repeats itself as the embossing roll rotates through a distance equivalent to the circumference of the roll.

It also has been proposed to secure a matte effect on sheeting by subjecting the sheeting to certain surface oxidation treatments, by flame contact or the like. Such flame treatments, in addition to presenting possible hazards in the event the sheeting material is combustible or happens to have residual combustible solvent, may also cause a degradation of the sheeting. It has also been proposed to secure the translucent matte effect on the surface of the sheeting by depositing on the sheeting various materials exemplified by powdered glass or silica smoke. Such procedure, while producing translucency, creates somewhat higher internal reflection than an embossed surface'with accompanying reduction of transmission and is, therefore, disadvantageous in this respect. In addition, the introduction of powdered materials as aforementioned on to the surface of the sheeting presents problems of dulling the cutting tools in the event the resulting sheeting is to be subdivided or otherwise processed using cutting knives. Furthermore, when foreign materials are introduced into the surface of the sheet, scrap sheeting resulting from the fabrication of the sheets into other articles perhaps may not be subjected to scrap recovery because the foreign materials may completely pollute the scrap throughout the entire thickness of any product manufactured from the recovered scrap.

Numerous processes have been described wherein the surface of sheeting and even the entire sheets are subjected to chemical treatment with strong solvents or hydrolyzing agents which attack the sheeting material and thereby affect its appearance. Such hydrolysis methods, which in attacking the sheeting may cause the sheeting to lose strength or perhaps cause degradation are to be distinguished from the chemical-physical method of the present invention.

After extensive investigation, I have found a chemicalphysical method of treating the surface of sheets, plates, or the like items in a manner whereby a translucent or matte effect may be secured upon the surface to substantially any degree desired and without the permanent introduction into the sheet of foreign components.

This invention has for one object to provide a method for imparting a translucent or comparable surface to sheeting. Another object is to provide an improved chemical-physical process for treating sheeting whereby controlled translucent or matte effects may be secured on the surface of such sheets. Still another object is to provide a process of the class indicated which does not necessitate the permanent incorporation of foreign components in the sheeting. A still further object is to provide a new translucent type of sheeting wherein the surface of the sheeting imparting the translucency has a relatively uniformly changed surface but is still comprised of the same chemical materials as the remainder of the sheeting. Still another object is to provide a translucent sheeting which is of a character readily susceptible to scrap recovery therefrom. Other objects will appear hereinafter.

For a more complete understanding of my invention, reference is made to the attached drawings forming a part of this application. Figure 1 is a semidiagrammatic side elevation view of an apparatus arrangement such as might be used to overcoat and otherwise carry out the steps of my invention which will be described in detail hereinafter. Figure 2 is a sectional view on a tremendously large scale illustrating the appearance of the sheeting having an uncleared translucent surface in accordance with the present invention. Figure 3 is likewise a sectional view on a very large scale showing the partially cleared surface in accordance with the present invention.

Reference is now made to Figure 1 in which 2 represents a roll of sheeting, the surface of which is to be given a matte treatment in accordance with the present invention. This roll of starting material is supported in any conventional manner so that it may be unrolled in the direction of the arrow over the several idler rollers 3, 4, 5 and 6.

The last mentioned idler roll 6 is positioned with respect to a larger roller 7 in a relationship so that the sheeting passes underneath roller 7 into contact with the coating or subbing mechanism having the overall designation 8. This coating device 8 may be of conventional construction and includes, for example, a reservoir tank 9 for holding a coating liquid. The tank 9 has positioned therein a roller 10. These parts function in a manner that the passage of the sheeting under roller 7 and almost into contact with the small coating roller 10. That is, it is close enough to roller 10 to maintain a liquid bead when roller 10 is driven. This roller 10 may be power driven to cause it to rotate and continually pick up from container 9 the coating liquid and apply it to the sheet.

As indicated, this coating device 8 may be conventional and other types of coating devices such as hopper coaters and the like may be substituted.

The coated film upon leaving roller 7 passes to a heating or drying chamber given the overall designation 12. This drying or heating chamber 12 may merely be comprised of a suitably enclosed space provided with an inlet 13 for heated air and an outlet port 14 for exhausting the air or other heating medium and fumes from chamber 12. The chamber is provided with suitable openings at 15 and 16 for the entrance and withdrawal of the coated sheet. The interior of this chamber is provided with a plurality of idler rollers 18, 19, 29, 21, 22, 23 and 24, for example, whereby the coated slicet may be suitably looped or draped within the chamber 12 for most advantageously subjecting the coated sheet to the drying and heating operations which will be described in detail hereinafter. It is desirable to mention at this point that the distance between rollers 7, 18 and 19 is preferably such that the coating applied at parts 7 and 8 has an opportunity to sufficiently solidify before coming in contact with roller 19. It will be observed that at the point of contact with roller 19 the coated sheet has reverse direction and therefore the coated surface comes in contact with the roller. Therefore, if the coating has set to some extent, roller 19 cannot in any way injure the coating.

Referring now to the exit from the drying chamber 12, the sheet passes through opening 16 and then passes around a plurality of additional rollers 27, 28, 29 and 30 and to bring the sheet in contact with another coating or subbing device comprising roller 31 and 32 of a construction similar to parts 7, 8, 9 and already described. These parts function to apply a thin coating of clearing liquid to the sheeting as it passes underneath and around roller 32. The composition and purpose of this clearing liquid applied by mechanism 31 will be set forth in detail hereinafter.

The cleared sheet is conducted from roller 32 into another chamber 35 of a construction substantially identical with chamber 12 already described; That is, the chamber 35 is provided with inlets and outlets36 and 37 for a suitable heating or drying medium supplied to or withdrawn from chamber 35. Chamber 35 is provided with openings 38 and 39 whereby the sheet material may be introduced into the chamber and withdrawn from the chamber. The interior of the chamber is provided with a plurality of rollers such as at 41 for suitably looping the sheet within the chamber for best exposing it to the drying or curing medium. The finished sheet leaving through opening 39 passes over one or more rollers as at 42 and is then wound up in a conventional manner at 45. In order to move the sheeting through the apparatus, roll 45 will be power driven. The apparatus of Figure 1 illustrates one type of arrangement which may be used for the continuous carrying out of my invention.

Referring now to Figure 2 there is shown on a scale of magnification of the order of300 times what a photomicrograph of a cross-section of my sheet would appear as when emerging at point 16. The product is made up of a base portion 46, the surface and sub-surface of which contain numerou's -gas pockets as shown at 47.

Referring to Figure 3 which likewise'is a highly magnified crosssection such as'would be shown by a photomicrograph of my product as it emerges at point 39, here again the base is represented at 46. However, by partially clearing the surface, it will be observed that the gas pockets have been altered somewhat at 48.

As mentioned above, the term sheeting is used herein to mean in particular the fihns or foils well known on the commercial market for wrapping purposes, decorative articles, film base and the like. The exact thick ness of this sheeting is not material, and this invention contemplates the treatment of sheets which may be only a few lOOUths of an inch thick up to sheets which may be comparable to window glass and the like in thickness and configuration. Such sheeting is preferably made from material of cellulosic origin exemplified by cellulose esters as well as the various modified cellulosic materials. More particularly, mention may be made of cellulose acetate, cellulose propionate, cellulose butyrate or the mixed esters such as cellulose acetate butyrate to be referred to in detail hereinafter. There are also the cellulose ether type of materials which are fabricated into sheets. There is also the type of sheeting available commercially known as Vinylite and Pliofilm.

Inasmuch as the coating of sheeting of the class described and the formulation of cellulosic compositions or other compositions for preparing such preformed sheets is already known in the art, extended description thereof is unnecessary. It appears sufficient for the purposes of the present invention to mention that such sheets are frequently formed by coating a dope to the desired thickness on continuously rotating bands, coating wheels or the like, to cause the formation of the transparent or pigmented sheet after which the sheet is stripped from the coating apparatus, dried, cured, or otherwise processed, and wound up into rolls. The coating dopes may contain various pigments and/or dyes for coloring or other purposes and, therefore, the present invention embraces the treatment of pigmented sheets as well as transparent sheets for the purpose of securing a translucent surface efiect on such sheets.

The present invention is particularly applicable to the treatment of the surface of cellulose ester sheeting cx emplified by sheeting manufactured from cellulose acetate having an acetyl value from 28% to 44%, cellulose propionate, cellulose butyrate, or cellulose mixed esters such as cellulose acetate butyrate. Such cellulose ester sheeting may be from, for example, about of an inch thick to 4, of an inch or greater in thickness.

A general understanding of my invention will be had from a consideration of the following generic procedures concerning my invention. It was found that the surface of a preformed sheet, whether transparent or pigmented, may be given a translucent or ground glass appearance by overcoating either one or both surfaces of the sheet with coating liquids containing certain chemical materials which are substantially solvent insoluble (or not readily soluble) and which will decompose or sublime to gaseous products at temperatures below the softening point of the sheeting thus overcoated. The chemical material referred to above is preferably some kind of a salt that will readily decompose to liberate a relatively non-inflammable non-objectionable gas exemplified by carbon dioxide. The chemical is contained in a solvent, which will, to some extent, dissolve the surface of the sheeting being processed. This overcoating of the surface of the sheet with such a coating liquid, assuming that some type of carbonate is the salt being used, by virtue of the solvent penetrating or softening the surface of the sheeting, causes the carbonate to be deposited in or slightly below the surface of the sheeting.

That'is, by controlling the character of the solvent, the time of contact and the amount of the solvent and the like features, the inorganic chemiealcan be caused to penetrate the surface of the sheeting to any predetermined degree, thereby making it possible by this invention, as will be explained in further detail hereinafter, of procuring any predetermined and desired degree of transluccncy or matte effect.

The sheet thus overcoated is caused to dry or set suiiiciently so that it may be passed in contact with rollers or otherwise handled without damage in further processing described below.

The sheet thus overcoated and dried is then subjected to heating at a suitably elevated temperature for causing the decomposition or sublimation of the gas forming material which has thus penetrated the surface of the sheeting as just described and the liberation of the gas from the surface of the sheeting and/or just below the surface producing an effect on the surface and subsurface of the sheeting giving translucency. Since this effect is produced somewhat in a physical manner by the liberation of gases from and through the surface, the change in the surface of the sheeting is relatively uniform and without the repetition of defects such as may occur in processes employing a sand blasted roll for roughcning the surface of the sheet.

I have further found that the bestprocedure of operation is to use an amount of decomposable chemical and otherwise carry out the steps which have just been described to an extent that there is imparted to the surface of the sheeting a greater degree of translucency or opacity than may be finally desired or needed. Thereafter I have found that this sheeting having a greater degree of opacity than desired may be further treated to clear partially this translucent layer by means of applying to the treated surface of the sheet certain solvents in a small amount.

This subsequent solvent treatment referred to as partially clearing the matte surface and which is applied to the matte surface of the sheet after the decomposable or sublimable chemicals mentioned above has been removed to a substantial extent, seems to function in the following manner. That is, the partial clearing of the matte surface by the application of a solvent sub to the surface appears to collapse some of the gas holes in the surface of the sheet (presumably produced by the escaping gas) or the gas holes in the sublayer adjacent to the surface of the sheet in a manner as to lower the internal reflection of the sheeting but without reducing the surface roughness of the sheet produced in accordance with my invention to the point where dilfusion or translucency is lost.

From the foregoing general description it is believed that it can be seen that the broader aspects of my invention contemplate the processing of the surface or surfaces of various types of cellulosic sheeting with an overcoating liquid containing certain decomposable chemicals which may be caused to liberate a preferably non-toxic noninfiammable or otherwise innocuous gas. The process of liberating the overcoating materials from the surface of the sheet not only frees the sheet of the chemical materials which have been added to the sheet in the first steps, but gives the surface of the sheet and/or the sublayers immediately adjacent the surface of the sheet a suitable roughness or other similar configuration which imparts to the surface of the sheet the desired translucency or ground glass effect. Thereafter, this initial translucency effect may be altered and improved by subjecting the sheet to a suitable subbing operation which acts upon the minute gas holes produced by the escaping gas aforementioned, but yet still permits the maintenance of translucency on the surface of the sheet.

It is believed from the foregoing description that it can be appreciated that the resultant translucent sheet secured has a more uniform and predetermined degree of translucency than sheets heretofore produced by prior art methods.

A further understanding of my invention will be had from a consideration of the following specific examples which are set forth primarily for illustrating certain embodiments of my invention and are not to be construed as an undue limitation thereupon.

Example 1 i In accordance with this example, the sheeting which was treated to impart a translucent surface thereto is known as cellulose acetate sheeting. Such type sheeting is commercially obtainable and is comprised of cellulose acetate plasticized with diethyl phthalate and triphenyl phosphate.

This sheeting processed in accordance with this Example 1 was about .005 inch in thickness. The roll of sheeting to be treated was maintained in a conventional unreeling or unwinding mechanism as at 2 in Fig. 1, the free end being threaded through the apparatus and finally around a power-driven take-up mandrel as at 45. In the passage of the sheeting from unwinding to take up, the glossy surface of the sheet passed in contact with a coating mechanism as at 7, 8, 9, and of Fig. 1 extending across the complete width of the sheet. From this mechanism there was applied to the glossy surface of the sheeting a liquid of the following composition:

7 Percent (11) A fine grind of ammonium carbonate 9.45 (b) High viscosity cellulose acetate (37% acetyl) 1.8 (c) Methanol 7 (d) Monomethyl glycol ether (solvent) 15 (e) Ethylene dichloride (solvent), balance to make The liquid thus applied as an overcoating was applied so thin as to give merely a barely perceptible overcoating, 5-7/ 100,000",.

This coating was set up or preliminarily dried in its passage from roller 18 to roller 19 (see Fig. 1).

The overcoating thus applied and set then continued to pass through heating chamber 12 at a temperature of slightly in excess of 150 F. The gases escaping this heating were exhausted through 14.

From the heating step the sheeting now having a translucent surface passed to beneath roll 32 and from mechanism 31 there was applied a very minute sublayer comprised of 100% methanol which partially cleared and improved the translucent surface.

Thereafter a further drying and curing step was applied in 35 and the resultant finished translucent sheeting wound up on the take-up mandrel 45.

Example 2 In accordance with this example, a pigmented cellulose ester sheeting pigmented with a small amount of titanium dioxide having a glossy surface was processed in accord ance with my invention to provide a translucent surface thereon. This pigmented sheet which was in thickness, was overcoated with a coating composition similar to the composition set forth in detail under Example l, with the exception that the decomposable salt was comprised of ammonium bicarbonate. The ammonium bicarbonate was of a commercially obtainable technical grade and of the usual powdery nature.

The pigmented sheet thus overcoated was dried and the bicarbonate decomposed in a chamber such as the chamber 12 described in connection with Fig. 1. A pigmented sheet having a translucent nonglossy surface was obtained. This surface was partially cleared by treatment with a clearing solution comprised of a small amount of acetone diluted with water. It is desired to explain at this point that the degree of clearing the surface of the sheet can be controlled by the choice of the solvent used for the clearing solution. hat is, for example, an 8020 mixture of acetone in water will fairly rapidly and deeply attack a cellulose ester sheeting. On the other hand methanol alone may be regarded as milder in action. Hence, by choosing dififerent combinations of methanol, water and acetone, it is possible to partially clear the surface of the sheet to any desired degree.

Example 5' In connection with this example, the sheeting which was treated comprised a mixed ester sheet. That is, a cellulose acetate butyrate sheet of 9 thickness was supplied with an overcoating in accordance with the general procedure set forth in Example 1. The overcoating was made up of a fine grind of ammonium carbonate mixed with small amounts of dissolved acetate butyrate in a liquid vehicle. This caused a deposit on the cellulose acetate butyrate sheeting of the ammonium carbonate together with a thin coating of acetate butyrate.

The acetate butyrate sheet thus overcoated was subjected to the drying and heating for decomposing the salt as described in the preceding examples. Since a carbonate salt was used, a temperature between and F. sufliced. There resulted an acetae butyrate sheet having a translucent surface.

In accordance with this example, the sheeting treated was commercially known as a Vinylite sheeting. This sheeting is comprised of a copolymer made up of vinyl chloride and vinyl acetate. One surface of this sheet was overcoated with a coating solution comprising amounts of ammonium carbonate comparable to that described in Example 1 contained in an overcoating liquid made up of ethyl acetate having a small amount of Vinylite dissolved therein. There was obtained from this operation a Vinylite sheet with a thin layer or overcoating on one surface comprised of the dissolved Vinylite and ammonium carbonate. The overcoated Vinylite sheet was then subjected to drying and heating for decomposition of the salt to produce a sheet having a translucent surface. -The translucent surface was partially cleared with an aqueous solution of ethyl acetate solvent diluted with water. Here again by controlling the dilution of the ethyl acetate with water, the depth of clearingof the matte surface may be controlled.

Example 5 In accordance with this example, there was treated a cellulose ester sheeting of the type used in the photographic industry for movie film leader. That is, on movie film there is provided what is known as a leader strip at the start or finish of the roll of film. This leader strip, which prior to the present invention has been comprised of highly pigmented film stock, has for one purpose to prevent high glare from the projection screen at the start and finish of a reel of film. Expressed in another way, if an entirely transparent leader strip is employed, there is practically no obstruction to the light of the projector passing therethrough. This would cause undue illumination on the screen at the start or finish of the projection of movie film. Therefore, it is desirable to provide some sort of a leader strip on the ends of the film exhibiting a density in excess of .3.

Therefore, the usual cellulose ester sheet, the same as comprising the film base for the projection portion of the film, was overcoated with a liquid of the following composition:

Percent Ammonium bicarbonate 9.45 High viscosity cellulose acetate 2.7 Methanol 7.0 Methyl Cellosolve solvent 15.0 Ethylene dichloride solvent The balance This movie film sheet material, which it will be noted in this example, was thus overcoated and subjected to the drying and decomposing operations in a closed chamber comparable to chamber 12 of Fig. 1. There resulted a sheet material having translucent surfaces on both sides of the sheet. That is, the translucent surfaces were given a very slight partial clearing by means of treatment with aqueous methanol acetone clearing liquid. After drying and finally curing the sheet stock in a chamber comparable to chamber 35 of Fig. 1, this movie film type of stock now provided with translucency on both surfaces was cut and perforated, etc., into leader strips of movie film. This type of strip was particularly advantageous in that since the material contained no foreign components, there was, of course, nothing which would dull the cutting and perforating machinery. In addition, since the leader strip consisted of exactly the same sheeting composition as the film base of the projection strip to which the leader was attached, scrap recovery was simplified. The leader strip thus produced in accordance with my invention exhibited a density of approximately .34 and in addition exhibited the further advantage over the leader strips heretofore used in that the leader strip applied in accordance with the present example presents surfaces upon which identification can be written and also comprises a material which can be spliced without smearing of the splicing block.

Example 6 In accordance with this example, there was produced a translucent sheet useful in topographic work. A cellulose ester sheet of the type referred to in Example 1 was overcoated with a coating liquid of the following composition:

Percent Ground glass 3.50 Cellulose acetate 5.75

Gelatin 0.25 Acetic acid 1.0 Ammonium bicarbonate 1.0

Water 1.0 Methyl Cellosolve 14.00 Methanol 3.50 Acetone 70.00

The sheet thus overcoated was subjected to heating for decomposing the salt and to the other steps already de scribed in detail in connection with the sheeting examples with the resultant production of a sheet having a translucent surface. This surface would take ink or pencil without smearing and is, therefore, useful for topographic work. The cured sheet prepared in accordance with my invention conformed to topographic standards as respects shrinkage and the like.

Example 7 In accordance with this example, a photographic type of sheeting was treated. This sheeting was made up of a cellulose acetate base of about .005 thickness. This base carried a thin coating of gelatin, which gelatin coating carried a coating of glue, the glue layer carried a very thin coating of the order of .003" thickness of cellulose nitrate. The photographic base sheet of the character just described was overcoated with an overcoating of the thickness of the order of .00002" in accordance with the present invention. This ove-rcoating composition and its manner of application was in accordance with the details set forth in Example 1, the difference of this example from Example 1 being in the specific make-up of the base sheet being treated.

The photographic base sheet thus overcoated was subjected to :drying, heating for decomposing the salt, etc., to produce a composite photographic sheet having a translucent surface without the necessity of incorporating ground glass.

It may be seen from the above examples that 1 have found a relatively simple inexpensive method for producing sheeting having a translucent surface. While in the above examples, frequent reference has been made to the use of ammonium carbonate, or bicarbonate, as the decomposing salt, such salt being preferred because of its low cost and the easewith which it is decomposed, other chemicals may be used.

Examples of other decomposable or sublimable chemicals which may be used are as follows:

Ammonium carbamate having a formula NHaCOzNHz. This chemical sublimes at approximately 60 C. There may be also mentioned ammonium benzoate subliming at 160 C. and ammonium salicylates. There may also be mentioned ammonium hydrosulfide having a formula NHdSH which decomposes at approximately C. However, such sulfur-containing decomposable chemicals are not recommended, when compared with the ammonium carbonates because such sulfur-containing chemicals are prone to give off hydrogen sulfides. As is well known, such sulfide gases are ill-smelling and otherwise present problems of handling. In general, any chemical that may be incorporated in a solvent as above described may be used and which sublime and/or decompose to non-injurious gaseous products, at temperatures below those which would be damaging to the sheeting may be used in the process of the present invention. In genenal, however, I prefer its use to salts which decompose at relatively low temperatures say between 140 F. to 250 F. and thereby simplify the heating problems. The term decompose is used herein to embrace such action. When the term gas is used it embraces the liberation of one or more gases. That is, in the instance of ammonium bicarbonate both ammonia and carbon dioxide would be evolved.

Likewise, while I have in the above examples frequently referred to the use of an alcohol and acetone for partially clearing the translucent surface in the last steps of my process in view of the simplicity and ready commercial [availability of such solvents it is to be understood that other diluted ketones, hydrocarbons, and ethyl acetate may be used in a similar manner. That is, solvents such as ethyl acetate are useful when processing the vinyl type of sheeting.

I have provided a new translucent sheeting characterized in that the surface effect for giving translucency is much more uniform and regular in that it has been obtained both in the surface and subsurface by liberation of gas breaking up or roughening the sheet surface. In addition, as already described, this characteristic surface has been modified by means of the solvent subbing which collapses certain of the gas holes.

My translucent sheeting is useful for any of the purposes for which translucent sheeting has been heretofore used in the art, and is particularly useful for purposes such as leader strips, topographic purposes, and for certain types of photographic purposes.

I claim:

1. A process of preparing 1a translucent cellulosic sheet, the surfaces of such sheet having a matte or ground glass appearance of exceptional regularity and uniformity which comprises treating the surface of a preformed cellulosic sheet from the group consisting of cellulose acetate sheets, cellulose propionate acetate sheets, cellulose butyrate acetate sheets, and mixed cellulose ester sheets, with a liquid which is a solvent for the surface of the sheet and will soften the surface, said liquid containing as an essential ingredient an ammonium chemical which is substiantially insoluble in the solvent and which chemical compound will decompose to gaseous products at a temperature below a temperature which is destructive of the sheeting being treated, to overcoat the sheet, subjecting the sheet thus overcoated to an elevated temperature between 140 F. and 250 F. for a suflicient'period to cause the decomposition of a substantial proportion of said chemical with gas liberation, whereby said gas liberation causes :gas holes in the overcoated layer and immediately a djacent sublayers of said sheet thereby producing a uniform and regular roughness. on the surface of the sheet for securing opacity and translucency.

2. A process of preparing a plastic sheet wherein at least one of the surfaces of such sheet has a translucent appearance of excellent regularity and uniformity which comprises ouercoating the surface of the sheet which it is desired to impart translucency thereto with an overcoating which contains as an essential ingredient a chemical from the group consisting of ammonium carbonate and ammonium bicarbonate which chemical will readily decompose to a gaseous product, said 'overcoating also containing a cellulose ester component, subjecting the sheet thus containing a chemical in its surface to a temperature between 140 F. and 250 F. for a sufficient period to cause the decomposition of a substantial proportion of said chemical with gas liberation, whereby said gas liberation causes gas holes in the surface layer and immediately adjacent subl ayers of said sheet thereby producing a uniform and regular roughness on the surface of the sheet for securing translucency and thereafter subjecting this translucent surface to la partial clearing by applying an alcoholic solvent thereto whereby a certain portion of the gas holes in the sublayers are collapsed for lowering 10 internal reflection without reducing the'surface roughness to such a point where diffusion is lost.

3. In a process of preparing translucent plastic sheets wherein at least one of the surfaces of such sheet has a matte or ground glass appearance of exceptional regularity and uniformity, the steps which comprise treating a preformed sheet with an organic liquid which is a solvent for the surface of the sheet and will soften the surface, said liquid containing as an essential ingredient an ammonium chemical which is relatively insoluble in the solvent and which chemical compound will decompose to a gaseous product at a temperature below a temperature which is destructive of the sheet being treated to overcoat the sheet, said liquid also containing a small content of plastic material of a composition compatible with the composition of said sheet whereby a thin overcoating of said sheet is obtained, subjecting the sheet thus overcoated to increased temperature between F. and 250 F., below the temperature destructive of the sheet for a sufiicient period to cause the decomposition of a substantial proportion of said chemical with gas liberation, whereby said gas liberation causes gas holes in the surface layer and immediately adjacent sublayers of said sheet thereby producing a uniform and regular roughness on the surface thereof for securing translucency.

4. The process of preparing a photographic film leader strip Which comprises subjecting a thin cellulosic flexible sheet to treatment on both surfaces with a coating liquid containing a decomposable ammonium salt and cellulose ester to provide a thin overcoating on both sides of the sheet in which the decomposable salt is entrapped, subjecting the sheet to heating between 140 F. and 250 F. for causing decomposition and removal of substantially all of the decomposable salt whereby a sheet is obtained having a translucency on both surfaces and thereafter employing the material produced as photographic leader strips.

5. A process of preparing a translucent sheet which comprises subjecting a preformed cellulosic sheet to treatment which includes contacting the surface of the sheet which it is desired to impart translucency thereto with a liquid which is an organic solvent for the surface of the cellulosic sheet and will soften the surface thereof, said liquid containing as an essential ingredient a chemical from the group consisting of ammonium carbonate and ammonium bicarbonate, which chemical compound will decompose to gaseous products at a temperature below :a temperature which is destructive of the cellulosic sheeting being treated, to overcoat the sheet, subjecting the sheet thus overcoated to a temperature between 140 F. and 250 F. for 1a suflicient period to cause the decomposition of a substantial proportion of the chemical salt with gas liberation, whereby said gas liberation causes gas holes in the surface layer and immediately adjacent sublayers of said cellulosic sheet thereby produc ing a uniform and regular roughness on the surface for securing translucency and thereafter subjecting this translucent surface to a partial clearing by treatment with a chemical liquid which is a solvent for the surface of the sheet treated as aforesaid, whereby a certain portion of the gas holes are collapsed for lowering internal reflection without reducing the surface roughness to such a point where diffusion is lost.

6. A process of preparing a plastic sheet wherein at least one of the surfaces of such sheet has a translucent, matte or ground glass appearance of exceptional regularity and uniformity which comprises subjecting a plastic sheet to treatment to overcoat the sheet, which treatment includes contacting the surface of the sheet which it is desired to impart translucency thereto, with a liquid composition, said liquid composition containing at least the two ingredients, a solvent for the surface of the sheet, said solvent having incorporated therein an 11 7 12 ammonium chemical, which ammonium chemical will References Cited in the file of this patent substantially completely decompose to a gaseous prod- UNITED STATES PATENTS net at a temperature within the range of 140? F, to 250 F., subjecting the sheet thus overcoated to an elevated g??? R temperature between 140 F. to 250 F. for a sufficient 5 2286'834 f 1 1942 period to cause the decomposition of at least a substan- 2332'031 T I .ouse 6 1943 tial proportion of the ammonium chemical with gas lib- 2367275 Z; mm I c 1945 eration, whereby said gas liberation causes gas holes in 2386626 N z s 1945 the surface layer and immediately adjacent sublayers of 2422423 a1 an c 1947 said sheet thereby producing auniform and regular rough- 10 2488588 xfles 1949 ness on the sheet surface for securing opacity and trans- 5 491 P 6 a 1951 lucency and thereafter subjecting this translucent sur- 2575046 igg i g; 55; 1951 face to a partlal clearing by applying thereto a hydroxy 2,628,945 Wayne Feb. 17 1953 solvent that is a solvent for the surface of the sheet roughened as aforesaid, whereby a certain portion of the gas holes in the sublayers are collapsed for lowering internal reflection without reducing thesuiface roughness to such a point where difiusion is lost.

1r 2,634,243 Glenn Aug. 7, 1953 

1. A PROCESS OF PREPARING A TRANSLUCENT CELLULOSIC SHEET, THE SURFACES OF SUCH SHEET HAVING A MATTE OR GROUND GLASS APPEARANCE OF EXCEPTIONAL REGULARITY AND UNIFORMITY WHICH COMPRISES TREATING THE SURFACE OF A PREFORMED CELLULOSIC SHEET FROM THE GROUP CONSISTING OF CELLULOSE ACETATE SHEETS, CELLULOSE PROPIONATE ACETATE SHEETS, CELLULOSE BUTYRATE ACETATE SHEETS, AND MIXED CELLULOSE ESTER SHEETS, WITH A LIQUID WHICH IS A SOLVENT FOR THE SURFACE OF THE SHEET AND WILL SOFTEN THE SURFACE, SAID LIQUID CONTAINING AS AN ESSENTIAL INGREDIENT AN AMMONIUM CHEMICAL WHICH IS SUBSTANTIALLY INSOLUBLE IN THE SOLVENTAND WHICH CHEMICALLY COMPOUND WILL DECOMPOSE TO GASEOUS PRODUCTS AT A TEMTERATURE BELOW A TEMPERATURE WHICH IS DESTRUCTIVE OF THE SHEETING BEING TREATED, TO OVERCOAT THE SHEET, SUBJECTING THE SHEET THUS OVERCOATED TO AN ELEVATED TEMPERATURE BETWEEN 140* F. AND 250* F. FOR A SUFFICIENT PERIOD TO CAUSE THE DECOMPOSITION OF A SUBSTANTIAL PROPORTION OF SAID CHEMICAL WITH GAS LIBERATION, WHEREBY SAID GAS LIBERATION CAUSES GAS HOLES IN THE OVERCOATED LAYER AND IMMEDIATELY ADJACENT SUBLAYERS OF SAID SHEET THEREBY PRODUCING A UNIFORM AND REGULAR ROUGHNESS ON THE SURFACE OF THE SHEET FOR SECURING OPACITY AND TRANSLUCENCY. 